Bottle nipple keeps clogging!! Help!!

Hillary

I exclusively pump and I use the Dr. Browns bottles. Lately with every bottle I feed my daughter the nipple gets clogged multiple times throughout the feeding. I have noticed that after I pump and I pour the milk into the bottles that there is a lot of chunks of fat. Is there any way to minimize it or mix it better? I do swirl the milk around in the bottle but it’s still separated. It’s been driving me crazy and I’m not sure what to do!